Processing

The processing route involves the use of gravity separation and flotation to produce a high-purity concentrate that will contain about 90% (ninety percent) monazite.

A concentrate that contains copper, gold and silver will be produced as a by-product during this phase. The monazite concentrate will be chemically cleaned to remove residual apatite and sulphide contamination, after which it will be treated with caustic soda to render the rare earth elements soluble in a dilute acid solution.

The cerium and lanthanum will be removed from the mixed rare earth salts at the mine and will be refined for sale in South Africa. The cerium and lanthanum-depleted mixed rare earth carbonate could be sold to companies that separate the individual rare earth oxides.

Description and Design Parameters

The fundamental premise upon which the process plant design is based was the SMM requirement for an annual production of ±2 700tpa TREO+Y2O3 with production being increased to satisfy the market demand. The optimised process flow design for Phase 1 entails the following:

  • the delivery of the mined bulk material to surface RoM stockpiles, and
  • the transfer of the RoM and historic surface rock dumps and TSF material to the Metallurgical Plant (front end) which comprises
    • a front-end comminution circuit comprising a crusher plant, fines handling circuit and milling circuit
    • a concentrator plant comprising of gravity and flotation separation units which will produce a REE mineral concentrate feed for the Hydrometallurgical Plant

The optimised Hydrometallurgical Plant process flow design for Phase 2 entails the following:

  • an acid bake to produce a TREE sulphate solution from the REE mineral concentrate
  • a double TREE sulphate salt precipitation stage at which point the LREE and HREE concentrate streams separate
  • a caustic conversion of the TREE in the double salt precipitate to TREE hydroxides
  • a selective hydrochloric acid leach to remove cerium and thorium
  • removal of copper and other impurities from the HREE stream
  • removal of radium, lanthanum, and actinium from the LREE stream, and
  • precipitation of a cerium depleted mixed REE carbonate product from both purified streams.
Hydrometallurgical Schematic Diagram

Initially the Steenkampskraal Process Plant will be constructed in two Phases to reduce initial capital funding requirements.

The surface historic TSF material is a simple and readily available plant feed which can be treated at low operational costs and can provide early revenue for the project. Therefore, the strategic decision was made to construct the Hydrometallurgical Plant and milling circuit first, which will treat the historic feed to plat material in the first year of production, while the existing access decline into the underground mine is refurbished and equipped and the Metallurgical Plant is constructed to be ready for the treatment of the underground RoM once the mine is in operation.

  • ~5 400 tonnes per annum (base case) monazite concentrate will be produced in phase 1
  • Proven conventional gravity separation and flotation processing plant during phase 1, based on the successful Anglo American 1952-1963 processing plant
  • Test work by Mintek and pilot by the Saskatchewan Research Council
  • Cerium and lanthanum depleted mixed rare earth carbonate (“CDMREC”) and Thorium with associated daughter products (i.e. 228Ra for medical isotopes used in the treatment of various cancers) will be produced in phase 2
  • The separation of rare earth oxides are being investigated and the strategy is to implement the extraction as phase 3, and the process flowsheets are designed on technically robust, proven unit processes used in the mineral processing industry. The unit processes are however combined and housed in such a manner as to minimise the risk of radiation.